1. Field of the Invention
The present invention relates to an image forming optical system having arrays of fine picture elements and non-emission portions (masks) located between the picture elements which do not contribute to the formation of an image, and more precisely to an apparatus for decreasing contrast of the non-emission portions (masks).
2. Description of the Related Art
In a CRT, liquid crystal color TV or endoscope, an image is formed by arrays of fine picture elements. For instance, in a liquid crystal color TV, non-emissin portions (masks), which are usually black and which do not contribute to formation of an image, are located between the picture element arrays in order to increase the overall contrast. In an image formed by fine picture element arrays in optical fibers, black masks (light intercepting covers) are provided in spaces between the respective fibers. However, since such non-emission portions (masks) are provided microscopically in the form of black and white lines which appear between the fine picture elements projected or viewed through an ocula optical system, the lines tend to interfere with an image, particularly a white or other bright image. The tendency is more noticeable in a recent image forming optical system having arrays of finer picture elements, in comparison with a conventional image forming optical system in which the fine picture elements are sufficiently larger than the masks. Namely, the number of people who feel that the masks on the image are offensive is increasing. In the liquid crystal system, since a switching mechanism or the like is absolutely necessary, the reduction of the line width of the masks is restricted. On the other hand, picture elements must be made smaller.
Optical fibers have the same tendency, since the space occupied by the masks in the spaces between associated optical fibers relatively becomes large as the diameter of the optical fiber having a circular cross section decreases.
It is known to defocus an image in order to decrease the contrast of the masks. This is useful to some extent, but it is very difficult to uniformly defocus a whole image, similarly the difficulty in effecting the uniform elimination of aberration of an entire image. For example, if proper defocusing is peformed at the center portion of the image, either excess or insufficient defocus takes place at the circumferential portion of the image.
In a projecting optical system having a liquid crystal, it is possible to reduce the contrast of the masks to some extent by increasing the distance between the liquid crystal panel and the mask. This is, however, goes contrary to the need for the reduction in size and thickness of optical system.